From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: x86/kprobes: Fix crash when probing CS CALL instructions When using eBPF to probe CS CALL instructions within a function, a crash can be triggered. The eBPF tool probes offset 257 of the __hrtimer_run_queues() function: <__hrtimer_run_queues+249>: nopl 0x0(%rax,%rax,1) <__hrtimer_run_queues+254>: mov %r14,%rdi <__hrtimer_run_queues+257>: cs call <__x86_indirect_thunk_r12> <__hrtimer_run_queues+263>: mov %eax,%r12d <__hrtimer_run_queues+266>: xchg %ax,%ax <__hrtimer_run_queues+268>: mov %r13,%rdi Which triggers this crash: BUG: unable to handle page fault for address: 00000000000f41c9 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#1] SMP NOPTI CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P RIP: 0010:__hrtimer_run_queues+0x106/0x230 Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is at the 6th byte of the above CS CALL instruction. Since the CS CALL instruction occupies 6 bytes, the exception occurred in the middle of that call instruction. The root cause is that when using eBPF tools to probe in the middle of a function, a kprobe with INT3 is used as the underlying implementation. During single-step emulation of the original CALL instruction, int3_emulate_call() assumes that the probed CALL instruction is 5 bytes long. However, the actual CS-prefixed CALL instruction occupies 6 bytes, so it constructs an incorrect exception return address. When the CPU returns from the kprobe handler, the next instruction to be executed is at the address of the last byte of that CS CALL instruction. Coincidentally, starting from that address, the CPU fetches and decodes a completely different instruction, which ultimately triggers a kernel crash. Fix the issue by using the actual instruction length obtained from the instruction decoder when constructing the exception return address, rather than relying on the hardcoded CALL_INSN_SIZE macro. [ mingo: Refined the changelog ] Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step") Suggested-by: Masami Hiramatsu (Google) Signed-off-by: Jinke Han Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Acked-by: Yafang Shao Acked-by: Borislav Petkov Cc: Peter Zijlstra Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000 --- drivers/input/misc/xen-kbdfront.c | 572 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 572 insertions(+) create mode 100644 drivers/input/misc/xen-kbdfront.c (limited to 'drivers/input/misc/xen-kbdfront.c') diff --git a/drivers/input/misc/xen-kbdfront.c b/drivers/input/misc/xen-kbdfront.c new file mode 100644 index 000000000..6471d836f --- /dev/null +++ b/drivers/input/misc/xen-kbdfront.c @@ -0,0 +1,572 @@ +/* + * Xen para-virtual input device + * + * Copyright (C) 2005 Anthony Liguori + * Copyright (C) 2006-2008 Red Hat, Inc., Markus Armbruster + * + * Based on linux/drivers/input/mouse/sermouse.c + * + * This file is subject to the terms and conditions of the GNU General Public + * License. See the file COPYING in the main directory of this archive for + * more details. + */ + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include +#include +#include +#include +#include +#include + +#include + +#include +#include +#include +#include +#include +#include +#include +#include +#include + +struct xenkbd_info { + struct input_dev *kbd; + struct input_dev *ptr; + struct input_dev *mtouch; + struct xenkbd_page *page; + int gref; + int irq; + struct xenbus_device *xbdev; + char phys[32]; + /* current MT slot/contact ID we are injecting events in */ + int mtouch_cur_contact_id; +}; + +enum { KPARAM_X, KPARAM_Y, KPARAM_CNT }; +static int ptr_size[KPARAM_CNT] = { XENFB_WIDTH, XENFB_HEIGHT }; +module_param_array(ptr_size, int, NULL, 0444); +MODULE_PARM_DESC(ptr_size, + "Pointing device width, height in pixels (default 800,600)"); + +static void xenkbd_remove(struct xenbus_device *); +static int xenkbd_connect_backend(struct xenbus_device *, struct xenkbd_info *); +static void xenkbd_disconnect_backend(struct xenkbd_info *); + +/* + * Note: if you need to send out events, see xenfb_do_update() for how + * to do that. + */ + +static void xenkbd_handle_motion_event(struct xenkbd_info *info, + struct xenkbd_motion *motion) +{ + if (unlikely(!info->ptr)) + return; + + input_report_rel(info->ptr, REL_X, motion->rel_x); + input_report_rel(info->ptr, REL_Y, motion->rel_y); + if (motion->rel_z) + input_report_rel(info->ptr, REL_WHEEL, -motion->rel_z); + input_sync(info->ptr); +} + +static void xenkbd_handle_position_event(struct xenkbd_info *info, + struct xenkbd_position *pos) +{ + if (unlikely(!info->ptr)) + return; + + input_report_abs(info->ptr, ABS_X, pos->abs_x); + input_report_abs(info->ptr, ABS_Y, pos->abs_y); + if (pos->rel_z) + input_report_rel(info->ptr, REL_WHEEL, -pos->rel_z); + input_sync(info->ptr); +} + +static void xenkbd_handle_key_event(struct xenkbd_info *info, + struct xenkbd_key *key) +{ + struct input_dev *dev; + int value = key->pressed; + + if (test_bit(key->keycode, info->ptr->keybit)) { + dev = info->ptr; + } else if (test_bit(key->keycode, info->kbd->keybit)) { + dev = info->kbd; + if (key->pressed && test_bit(key->keycode, info->kbd->key)) + value = 2; /* Mark as autorepeat */ + } else { + pr_warn("unhandled keycode 0x%x\n", key->keycode); + return; + } + + if (unlikely(!dev)) + return; + + input_event(dev, EV_KEY, key->keycode, value); + input_sync(dev); +} + +static void xenkbd_handle_mt_event(struct xenkbd_info *info, + struct xenkbd_mtouch *mtouch) +{ + if (unlikely(!info->mtouch)) + return; + + if (mtouch->contact_id != info->mtouch_cur_contact_id) { + info->mtouch_cur_contact_id = mtouch->contact_id; + input_mt_slot(info->mtouch, mtouch->contact_id); + } + + switch (mtouch->event_type) { + case XENKBD_MT_EV_DOWN: + input_mt_report_slot_state(info->mtouch, MT_TOOL_FINGER, true); + fallthrough; + + case XENKBD_MT_EV_MOTION: + input_report_abs(info->mtouch, ABS_MT_POSITION_X, + mtouch->u.pos.abs_x); + input_report_abs(info->mtouch, ABS_MT_POSITION_Y, + mtouch->u.pos.abs_y); + break; + + case XENKBD_MT_EV_SHAPE: + input_report_abs(info->mtouch, ABS_MT_TOUCH_MAJOR, + mtouch->u.shape.major); + input_report_abs(info->mtouch, ABS_MT_TOUCH_MINOR, + mtouch->u.shape.minor); + break; + + case XENKBD_MT_EV_ORIENT: + input_report_abs(info->mtouch, ABS_MT_ORIENTATION, + mtouch->u.orientation); + break; + + case XENKBD_MT_EV_UP: + input_mt_report_slot_inactive(info->mtouch); + break; + + case XENKBD_MT_EV_SYN: + input_mt_sync_frame(info->mtouch); + input_sync(info->mtouch); + break; + } +} + +static void xenkbd_handle_event(struct xenkbd_info *info, + union xenkbd_in_event *event) +{ + switch (event->type) { + case XENKBD_TYPE_MOTION: + xenkbd_handle_motion_event(info, &event->motion); + break; + + case XENKBD_TYPE_KEY: + xenkbd_handle_key_event(info, &event->key); + break; + + case XENKBD_TYPE_POS: + xenkbd_handle_position_event(info, &event->pos); + break; + + case XENKBD_TYPE_MTOUCH: + xenkbd_handle_mt_event(info, &event->mtouch); + break; + } +} + +static irqreturn_t input_handler(int rq, void *dev_id) +{ + struct xenkbd_info *info = dev_id; + struct xenkbd_page *page = info->page; + __u32 cons, prod; + + prod = page->in_prod; + if (prod == page->in_cons) + return IRQ_HANDLED; + rmb(); /* ensure we see ring contents up to prod */ + for (cons = page->in_cons; cons != prod; cons++) + xenkbd_handle_event(info, &XENKBD_IN_RING_REF(page, cons)); + mb(); /* ensure we got ring contents */ + page->in_cons = cons; + notify_remote_via_irq(info->irq); + + return IRQ_HANDLED; +} + +static int xenkbd_probe(struct xenbus_device *dev, + const struct xenbus_device_id *id) +{ + int ret, i; + bool with_mtouch, with_kbd, with_ptr; + struct xenkbd_info *info; + struct input_dev *kbd, *ptr, *mtouch; + + info = kzalloc_obj(*info); + if (!info) { + xenbus_dev_fatal(dev, -ENOMEM, "allocating info structure"); + return -ENOMEM; + } + dev_set_drvdata(&dev->dev, info); + info->xbdev = dev; + info->irq = -1; + info->gref = -1; + snprintf(info->phys, sizeof(info->phys), "xenbus/%s", dev->nodename); + + info->page = (void *)__get_free_page(GFP_KERNEL | __GFP_ZERO); + if (!info->page) + goto error_nomem; + + /* + * The below are reverse logic, e.g. if the feature is set, then + * do not expose the corresponding virtual device. + */ + with_kbd = !xenbus_read_unsigned(dev->otherend, + XENKBD_FIELD_FEAT_DSBL_KEYBRD, 0); + + with_ptr = !xenbus_read_unsigned(dev->otherend, + XENKBD_FIELD_FEAT_DSBL_POINTER, 0); + + /* Direct logic: if set, then create multi-touch device. */ + with_mtouch = xenbus_read_unsigned(dev->otherend, + XENKBD_FIELD_FEAT_MTOUCH, 0); + if (with_mtouch) { + ret = xenbus_write(XBT_NIL, dev->nodename, + XENKBD_FIELD_REQ_MTOUCH, "1"); + if (ret) { + pr_warn("xenkbd: can't request multi-touch"); + with_mtouch = 0; + } + } + + /* keyboard */ + if (with_kbd) { + kbd = input_allocate_device(); + if (!kbd) + goto error_nomem; + kbd->name = "Xen Virtual Keyboard"; + kbd->phys = info->phys; + kbd->id.bustype = BUS_PCI; + kbd->id.vendor = 0x5853; + kbd->id.product = 0xffff; + + __set_bit(EV_KEY, kbd->evbit); + for (i = KEY_ESC; i < KEY_UNKNOWN; i++) + __set_bit(i, kbd->keybit); + for (i = KEY_OK; i < KEY_MAX; i++) + __set_bit(i, kbd->keybit); + + ret = input_register_device(kbd); + if (ret) { + input_free_device(kbd); + xenbus_dev_fatal(dev, ret, + "input_register_device(kbd)"); + goto error; + } + info->kbd = kbd; + } + + /* pointing device */ + if (with_ptr) { + unsigned int abs; + + /* Set input abs params to match backend screen res */ + abs = xenbus_read_unsigned(dev->otherend, + XENKBD_FIELD_FEAT_ABS_POINTER, 0); + ptr_size[KPARAM_X] = xenbus_read_unsigned(dev->otherend, + XENKBD_FIELD_WIDTH, + ptr_size[KPARAM_X]); + ptr_size[KPARAM_Y] = xenbus_read_unsigned(dev->otherend, + XENKBD_FIELD_HEIGHT, + ptr_size[KPARAM_Y]); + if (abs) { + ret = xenbus_write(XBT_NIL, dev->nodename, + XENKBD_FIELD_REQ_ABS_POINTER, "1"); + if (ret) { + pr_warn("xenkbd: can't request abs-pointer\n"); + abs = 0; + } + } + + ptr = input_allocate_device(); + if (!ptr) + goto error_nomem; + ptr->name = "Xen Virtual Pointer"; + ptr->phys = info->phys; + ptr->id.bustype = BUS_PCI; + ptr->id.vendor = 0x5853; + ptr->id.product = 0xfffe; + + if (abs) { + __set_bit(EV_ABS, ptr->evbit); + input_set_abs_params(ptr, ABS_X, 0, + ptr_size[KPARAM_X], 0, 0); + input_set_abs_params(ptr, ABS_Y, 0, + ptr_size[KPARAM_Y], 0, 0); + } else { + input_set_capability(ptr, EV_REL, REL_X); + input_set_capability(ptr, EV_REL, REL_Y); + } + input_set_capability(ptr, EV_REL, REL_WHEEL); + + __set_bit(EV_KEY, ptr->evbit); + for (i = BTN_LEFT; i <= BTN_TASK; i++) + __set_bit(i, ptr->keybit); + + ret = input_register_device(ptr); + if (ret) { + input_free_device(ptr); + xenbus_dev_fatal(dev, ret, + "input_register_device(ptr)"); + goto error; + } + info->ptr = ptr; + } + + /* multi-touch device */ + if (with_mtouch) { + int num_cont, width, height; + + mtouch = input_allocate_device(); + if (!mtouch) + goto error_nomem; + + num_cont = xenbus_read_unsigned(info->xbdev->otherend, + XENKBD_FIELD_MT_NUM_CONTACTS, + 1); + width = xenbus_read_unsigned(info->xbdev->otherend, + XENKBD_FIELD_MT_WIDTH, + XENFB_WIDTH); + height = xenbus_read_unsigned(info->xbdev->otherend, + XENKBD_FIELD_MT_HEIGHT, + XENFB_HEIGHT); + + mtouch->name = "Xen Virtual Multi-touch"; + mtouch->phys = info->phys; + mtouch->id.bustype = BUS_PCI; + mtouch->id.vendor = 0x5853; + mtouch->id.product = 0xfffd; + + input_set_abs_params(mtouch, ABS_MT_TOUCH_MAJOR, + 0, 255, 0, 0); + input_set_abs_params(mtouch, ABS_MT_POSITION_X, + 0, width, 0, 0); + input_set_abs_params(mtouch, ABS_MT_POSITION_Y, + 0, height, 0, 0); + + ret = input_mt_init_slots(mtouch, num_cont, INPUT_MT_DIRECT); + if (ret) { + input_free_device(mtouch); + xenbus_dev_fatal(info->xbdev, ret, + "input_mt_init_slots"); + goto error; + } + + ret = input_register_device(mtouch); + if (ret) { + input_free_device(mtouch); + xenbus_dev_fatal(info->xbdev, ret, + "input_register_device(mtouch)"); + goto error; + } + info->mtouch_cur_contact_id = -1; + info->mtouch = mtouch; + } + + if (!(with_kbd || with_ptr || with_mtouch)) { + ret = -ENXIO; + goto error; + } + + ret = xenkbd_connect_backend(dev, info); + if (ret < 0) + goto error; + + return 0; + + error_nomem: + ret = -ENOMEM; + xenbus_dev_fatal(dev, ret, "allocating device memory"); + error: + xenkbd_remove(dev); + return ret; +} + +static int xenkbd_resume(struct xenbus_device *dev) +{ + struct xenkbd_info *info = dev_get_drvdata(&dev->dev); + + xenkbd_disconnect_backend(info); + memset(info->page, 0, PAGE_SIZE); + return xenkbd_connect_backend(dev, info); +} + +static void xenkbd_remove(struct xenbus_device *dev) +{ + struct xenkbd_info *info = dev_get_drvdata(&dev->dev); + + xenkbd_disconnect_backend(info); + if (info->kbd) + input_unregister_device(info->kbd); + if (info->ptr) + input_unregister_device(info->ptr); + if (info->mtouch) + input_unregister_device(info->mtouch); + free_page((unsigned long)info->page); + kfree(info); +} + +static int xenkbd_connect_backend(struct xenbus_device *dev, + struct xenkbd_info *info) +{ + int ret, evtchn; + struct xenbus_transaction xbt; + + ret = gnttab_grant_foreign_access(dev->otherend_id, + virt_to_gfn(info->page), 0); + if (ret < 0) + return ret; + info->gref = ret; + + ret = xenbus_alloc_evtchn(dev, &evtchn); + if (ret) + goto error_grant; + ret = bind_evtchn_to_irqhandler(evtchn, input_handler, + 0, dev->devicetype, info); + if (ret < 0) { + xenbus_dev_fatal(dev, ret, "bind_evtchn_to_irqhandler"); + goto error_evtchan; + } + info->irq = ret; + + again: + ret = xenbus_transaction_start(&xbt); + if (ret) { + xenbus_dev_fatal(dev, ret, "starting transaction"); + goto error_irqh; + } + ret = xenbus_printf(xbt, dev->nodename, XENKBD_FIELD_RING_REF, "%lu", + virt_to_gfn(info->page)); + if (ret) + goto error_xenbus; + ret = xenbus_printf(xbt, dev->nodename, XENKBD_FIELD_RING_GREF, + "%u", info->gref); + if (ret) + goto error_xenbus; + ret = xenbus_printf(xbt, dev->nodename, XENKBD_FIELD_EVT_CHANNEL, "%u", + evtchn); + if (ret) + goto error_xenbus; + ret = xenbus_transaction_end(xbt, 0); + if (ret) { + if (ret == -EAGAIN) + goto again; + xenbus_dev_fatal(dev, ret, "completing transaction"); + goto error_irqh; + } + + xenbus_switch_state(dev, XenbusStateInitialised); + return 0; + + error_xenbus: + xenbus_transaction_end(xbt, 1); + xenbus_dev_fatal(dev, ret, "writing xenstore"); + error_irqh: + unbind_from_irqhandler(info->irq, info); + info->irq = -1; + error_evtchan: + xenbus_free_evtchn(dev, evtchn); + error_grant: + gnttab_end_foreign_access(info->gref, NULL); + info->gref = -1; + return ret; +} + +static void xenkbd_disconnect_backend(struct xenkbd_info *info) +{ + if (info->irq >= 0) + unbind_from_irqhandler(info->irq, info); + info->irq = -1; + if (info->gref >= 0) + gnttab_end_foreign_access(info->gref, NULL); + info->gref = -1; +} + +static void xenkbd_backend_changed(struct xenbus_device *dev, + enum xenbus_state backend_state) +{ + switch (backend_state) { + case XenbusStateInitialising: + case XenbusStateInitialised: + case XenbusStateReconfiguring: + case XenbusStateReconfigured: + case XenbusStateUnknown: + break; + + case XenbusStateInitWait: + xenbus_switch_state(dev, XenbusStateConnected); + break; + + case XenbusStateConnected: + /* + * Work around xenbus race condition: If backend goes + * through InitWait to Connected fast enough, we can + * get Connected twice here. + */ + if (dev->state != XenbusStateConnected) + xenbus_switch_state(dev, XenbusStateConnected); + break; + + case XenbusStateClosed: + if (dev->state == XenbusStateClosed) + break; + fallthrough; /* Missed the backend's CLOSING state */ + case XenbusStateClosing: + xenbus_frontend_closed(dev); + break; + } +} + +static const struct xenbus_device_id xenkbd_ids[] = { + { XENKBD_DRIVER_NAME }, + { "" } +}; + +static struct xenbus_driver xenkbd_driver = { + .ids = xenkbd_ids, + .probe = xenkbd_probe, + .remove = xenkbd_remove, + .resume = xenkbd_resume, + .otherend_changed = xenkbd_backend_changed, + .not_essential = true, +}; + +static int __init xenkbd_init(void) +{ + if (!xen_domain()) + return -ENODEV; + + /* Nothing to do if running in dom0. */ + if (xen_initial_domain()) + return -ENODEV; + + if (!xen_has_pv_devices()) + return -ENODEV; + + return xenbus_register_frontend(&xenkbd_driver); +} + +static void __exit xenkbd_cleanup(void) +{ + xenbus_unregister_driver(&xenkbd_driver); +} + +module_init(xenkbd_init); +module_exit(xenkbd_cleanup); + +MODULE_DESCRIPTION("Xen virtual keyboard/pointer device frontend"); +MODULE_LICENSE("GPL"); +MODULE_ALIAS("xen:" XENKBD_DRIVER_NAME); -- cgit v1.3.1